HAD - Hardware Activity Display
HAD (Hardware Activity Display) is a z/OS component that provides real-time and historical performance data for various hardware resources, including CPUs, channels, control units, and I/O devices. It is primarily used by system programmers and performance analysts to monitor system health, identify bottlenecks, and diagnose hardware-related performance issues within the mainframe environment.
Key Characteristics
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- Provides real-time and historical performance metrics for various hardware components, such as CPUs, channels, control units, and I/O devices.
- Offers a detailed, granular view of hardware utilization, including I/O rates, channel busy percentages, and device response times.
- Typically accessed via an ISPF-based interface, allowing system programmers to navigate through different hardware views and drill down into specific components.
- Utilizes data collected by z/OS performance monitors like RMF (Resource Measurement Facility) and internal system counters.
- Designed to be a low-overhead monitoring tool, minimizing its impact on the system being observed.
- Can display data for multiple LPARs (Logical Partitions) within a single sysplex environment, offering a consolidated view of hardware activity.
Use Cases
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- Identifying I/O Bottlenecks: Pinpointing specific channels, control units, or disk devices that are experiencing high utilization or long queue times, impacting overall system performance.
- Diagnosing Application Performance Issues: Correlating slow application response times with underlying hardware resource contention or failures, such as a heavily used disk volume.
- Capacity Planning: Analyzing historical hardware utilization trends to forecast future resource requirements and plan for upgrades or reconfigurations of I/O subsystems.
- Verifying Hardware Configuration Changes: Monitoring the impact of new hardware installations, channel path reconfigurations, or device migrations on system performance and stability.
- Proactive Monitoring: Establishing thresholds and alerts for critical hardware components to detect potential issues before they escalate into major outages or performance degradation.
Related Concepts
HAD is intrinsically linked to RMF (Resource Measurement Facility), often serving as a user-friendly interface to visualize and interpret the vast amounts of performance data collected by RMF. It complements SMF (System Management Facilities) by providing a real-time, interactive view of hardware metrics that might otherwise require batch processing of SMF records. HAD plays a crucial role in managing the I/O Subsystem, offering insights into channel path utilization, control unit activity, and device performance. Its data is vital for System Programmers and Performance Analysts to ensure the optimal functioning of LPARs and the entire z/OS environment.
- Regularly Monitor Key Metrics: Establish a routine for checking critical hardware metrics (e.g., channel busy, device response times, CPU utilization) to detect anomalies early.
- Establish Performance Baselines: Understand normal operating ranges for your hardware resources to quickly identify deviations that may indicate a problem or performance degradation.
- Correlate with Software Metrics: Always analyze HAD data in conjunction with software performance metrics (e.g., CPU utilization by address space, transaction rates from CICS or IMS) to get a complete picture of system health.
- Understand Your I/O Topology: Have a clear understanding of your channel paths, control units, and device configurations to accurately interpret HAD output and diagnose issues effectively.
- Utilize Historical Data for Trend Analysis: Leverage HAD's historical capabilities for long-term trend analysis, capacity planning, and identifying recurring performance patterns that require attention.